BK virus (BKV) and JC virus are recently recognized members of the SV40-polyoma subgroup of papovaviruses and they are common childhood infections. They remain latent after primary infection and are reactivated during times of immunological impairment. Like other members of the subgroup, they are oncogenic for laboratory animals. We will examine if these viruses are related etiologically to human tumors, particularly leukemic and lymphoid tumors, by immunofluorescence tests of tumor cells for virus coded T antigen and viral capsid antigens. The possibility that BKV is transmitted congenitally will be studied by tests of umbilical cord sera for virus-specific IgM antibodies. Serum specimens from transplant recipients will be tested for a rise in SV40 neutralizing antibodies and for SV40 IgM antibodies to determine if this virus is still active in human populations. Stumptailed macaque virus (STMV), a newly recognized simian papovavirus, appears to be transmitted congenitally. We will, therefore, examine if STMV-like or other papovaviruses are present in cell cultures derived from human fetal kidneys and from kidneys of other primates. Another simian virus, SA12, has been recently characterized as a new member of the subgroup. We will study by serologic tests the extent of distribution of SA12 infection in wild and laboratory-housed primates. Further, STMV and SA12 will be studied for their oncogenicity, transforming ability and immunologic relationships. An attempt will be made to determine the manner in which STMV is transmitted congenitally and to characterize the immunologic response of the host to this latent lifelong infection. DNAs of newly recognized papovaviruses will be studied for base sequence homologies with SV40 DNA to understand the evolutionary history of viruses of this subgroup. Together, these investigations will help in understanding the biology and pathogenic potential of these viruses.